Atomic Nuclei
- Page ID
- 37562
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Atoms - tiny wonders to explore
Atomic Nuclei
Some facts
Atomic radii: 1-3 Å (1e-10 m)
Nucleus radii: 1~3 fm (fermi or femtometer 1e-15 m)
- Protons
- Goldstein discovered canal rays (Kanalstrahlen) in 1886
- Wien and Thomson saw positive rays moving in opposite direction of cathode rays.
- Rutherford concluded that these are nuclei of H atoms, and he called them protons.
- Properties of protons:
charge, same as electron but positive
mass 1.67262314e-27 kg, mass of H less the electron mass
spin ½
magnetic moment, 2.7928474 nuclear magnetic moment
- Neutrons
- Rutherford speculated existence of neutral particles in atomic nuclei.
- Bothe, Becker, Joliot, Curie and Chadwick observed some very penetrating particles when they bombarded beryllium with alpha particles.
- The reaction is now known as
- Be + a = C + n + Energy
- James Chadwick (1891-1974) discovered and confirmed neutrons from the reaction
- B + n = Li + a + Energy
- Deuterium, an isotope of hydrogen
- Many scholars speculated the existence of isotopes
- Isotopes are atoms of the same element, but their masses are different.
Properties of H2, HD, and D2 Property H2 HD D2 Tripple point /K 13.96 16.60 18.73 Boiling point /K 20.39 22.13 23.67 - Nuclei of isotopes contain the same number of protons, but different number of neutrons
- Harold C. Urey (1893 - 1981) distilled H2 to get D2
- The abundance of D in hydrogen is 0.014%
- Electrolysis decomposes H2O faster than D2O, and the remaining water has a higher concentration of HDO and D2O than ordinary water (production of heavy water during WW II)
- Another isotope of H is tritium, T. Its nucleus contains 2 n and 1 p
- D is stable, but T emits beta particles
- Nuclide
A nuclide is represented by- MEZ
M, mass number; Z, atomic number (often omitted); N = M - Z is the number of neutrons
For example, 1H, 2H, and 3H are H, D, and T - Atomic weight average mass of all isotopes of an element.
Atomic mass of a nuclide is the mass of an isotope or nuclide. - Quarks
Protons and neutrons are composed of something smaller called quarks.
No individual quark has been observed, but theory and experiments suggest that proton consists of 2 up quarks and 1 down quark. A neutron consists of 1 up quark and 2 down quarks. - The standard model
Fundamental particles of the standard model Generation: First Second Third Quarks u, d c, s b, t Leptons e, ne m, nm t, nt
Contributors
Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)